9.3.2. Installation of the kernel
Building the kernel involves a few steps—configuration,
compilation, and installation. Read the README
file in the kernel source tree for
alternative methods to the way this book configures the kernel.
Prepare for compilation by running the following command:
make mrproper
This ensures that the kernel tree is absolutely clean. The kernel
team recommends that this command be issued prior to each kernel
compilation. Do not rely on the source tree being clean after
un-tarring.
Configure the kernel via a menu-driven interface. Please note that
the udev bootscript requires "rtc" and "tmpfs" to be enabled and
built into the kernel, not as modules. CBLFS has some information
regarding particular kernel configuration requirements of packages
outside of CLFS at http://cblfs.cross-lfs.org/:
make ARCH=i386 CROSS_COMPILE=${CLFS_TARGET}- menuconfig
Alternatively, make
oldconfig may be more appropriate in some
situations. See the README
file for
more information.
If desired, skip kernel configuration by copying the kernel config
file, .config
, from the host system
(assuming it is available) to the root directory of the unpacked
kernel sources. However, we do not recommend this option. It is
often better to explore all the configuration menus and create the
kernel configuration from scratch.
Compile the kernel image and modules:
make ARCH=i386 CROSS_COMPILE=${CLFS_TARGET}-
If using kernel modules, an /etc/modprobe.conf
file may be needed.
Information pertaining to modules and kernel configuration is
located in the kernel documentation in the Documentation
directory of the kernel sources
tree. Also, modprobe.conf(5)
may be
of interest.
Be very careful when reading other documentation relating to kernel
modules because it usually applies to 2.4.x kernels only. As far as
we know, kernel configuration issues specific to Hotplug and Udev
are not documented. The problem is that Udev will create a device
node only if Hotplug or a user-written script inserts the
corresponding module into the kernel, and not all modules are
detectable by Hotplug. Note that statements like the one below in
the /etc/modprobe.conf
file do not
work with Udev:
alias char-major-XXX some-module
Because of the complications with Udev and modules, we strongly
recommend starting with a completely non-modular kernel
configuration, especially if this is the first time using Udev.
Install the modules, if the kernel configuration uses them:
make ARCH=i386 CROSS_COMPILE=${CLFS_TARGET}- \
INSTALL_MOD_PATH=${CLFS} modules_install
After kernel compilation is complete, additional steps are required
to complete the installation. Some files need to be copied to the
${CLFS}/boot
directory.
Issue the following command to install the kernel:
cp arch/i386/boot/bzImage ${CLFS}/boot/clfskernel-2.6.30.1
System.map
is a symbol file for the
kernel. It maps the function entry points of every function in the
kernel API, as well as the addresses of the kernel data structures
for the running kernel. Issue the following command to install the
map file:
cp System.map ${CLFS}/boot/System.map-2.6.30.1
The kernel configuration file .config
produced by the make
menuconfig step above contains all the
configuration selections for the kernel that was just compiled. It
is a good idea to keep this file for future reference:
cp .config ${CLFS}/boot/config-2.6.30.1
Warning
Some kernel documentation recommends creating a symlink from
/usr/src/linux
pointing to the
kernel source directory. This is specific to kernels prior to the
2.6 series and must not be
created on an CLFS system as it can cause problems for packages
you may wish to build once your base CLFS system is complete.
Also, the headers in the system's include
directory should always be the ones against which
EGLIBC was compiled (from the Linux-Headers package) and should
never be replaced by the
kernel headers.